As one of a motor including a bearing bolder made of resin material JP3487066B discloses a motor, in which a bearing holder is integrally formed at one surface of a disc shaped brush holder. An outer diameter of the brush bolder is arranged to be entirely, or partially, larger than an inner diameter of a frame. An inner diameter of a bearing housing is arranged to be entirely, or partially, smaller than an outer diameter of the bearing. Further, thickness of the inner bearing holder is arranged to be one-third to one-half the thickness of the bearing.
Further, JP3266500B discloses a motor including a bearing rotatably supporting a shaft and a bearing holder for retaining the bearing. The bearing holder is made of thermoplastic resin including glass fiber and is formed by injection molding. A linear expansion coefficient in an axial direction of the motor is defined to be equal to or lower than 3.0×10−5/° C. Further, a linear expansion coefficient in a vertical direction relative to the axial direction is equal to or greater than the double of the linear expansion coefficient.
However, because compressive strength of the bearing holder made of the known resin material is lower than that of the bearing bolder made of metal material, a cylindrical portion of the bearing holder may be broken, or cracked, when press-fitting the bearing into the bearing holder. Therefore, in order to prevent the cylindrical portion of the bearing holder from being damaged (cracked), there is a requirement for high fitting dimensional accuracy between the bearing and the bearing holder and for a form designing and a manufacturing process taking into account a linear expansion of the resin material and a resin flow when molding the bearing holder. Further, there is a requirement for employing a resin material having high extension degree despite having inferior heat resistance and mechanical strength performance so as to prevent the cylindrical portion of the bearing holder from being damaged when press-fitting the bearing.
A need thus exists or a motor including a bearing holder, which is not susceptible to the drawback mentioned above.